Letter www.acsami.org
Hollow Porous Hierarchical-Structured 0.5Li2MnO3·0.5LiMn0.4Co0.3Ni0.3O2 as a High-Performance Cathode Material for Lithium-Ion Batteries Fang Fu, Jiayu Tang, Yuze Yao, and Minhua Shao* Department of Chemical and Biomolecular Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong S Supporting Information *
ABSTRACT: We report a novel hollow porous hierarchicalarchitectured 0.5Li2MnO3·0.5LiMn0.4Co0.3Ni0.3O2 (LLO) for lithium-ion batteries (LIBs). The obtained lithium-rich layered oxides possess a large inner cavity, a permeable porous shell, and excellent structural robustness. In LIBs, such unique features are favorable for fast Li+ transportation and can provide sufficient contact between active materials and electrolytes, accommodate more Li+, and improve the kinetics of the electrochemical reaction. The as-prepared LLO displays an extremely high initial discharge capacity (296.5 mAh g−1 at 0.2 C), high rate capability (162.6 mAh g−1 at 10 C), and excellent cycling stability (237.6 mAh g−1 after 100 cycles at 0.5 C and 153.8 mAh g−1 after 200 cycles at 10 C). These values are superior to most literature data. KEYWORDS: lithium-rich layered oxides, hollow porous structure, hierarchical architecture, cathode, stability, lithium-ion batteries
L
of lithium-rich layered oxides still cannot meet the needs for commercial applications. Because the properties of a material depend critically on its morphology and structure,11,12 engineering a novel structure is crucial to further improving the electrochemical performance of lithium-rich layered oxides. Hollow porous hierarchical (HPH) structures have attracted great attention for their intriguing structural features and great potential for various applications, especially in the field of LIBs. A HPH structure composed of a hollow interior and a porous shell not only provides good structural robustness and a short electron/ion diffusion pathway but also benefits electrolyte penetration and Li+ transport. These advantages are expected to significantly improve the electrochemical performance of electrode materials in LIBs. To the best of our knowledge, HPH-structured lithium-rich layered oxides have not been reported. Common morphologies of lithium-rich layered oxides are spherical, spherical-like, nanoplate, and irregular shape.13−16 Other reported types of structures and morphologies of this material are rather limited mainly because of their complex chemical compositions consisting of at least two transitionmetal elements. Structural and morphological control of lithium-rich layered oxides is difficult because of the dissimilar growth processes involved with different microscopic mechanisms and reaction rates.17,18 Thus, the controllable fabrication
ithium-ion batteries (LIBs) have revolutionized portable electronics and are primed to make a great impact on large-scale applications in energy storage and transportation. The energy and power densities of LIBs are highly dependent on the properties of their cathode materials.1−3 Thus, developing high-performance cathode materials with large reversible capacity and high rate capability is of great importance. Lithium-rich layered oxides, xLi2MnO3·(1 − x)LiMO2 (0 < x < 1; M = transition metal), have been identified as promising cathode candidates for future LIBs because of their high specific capacity (typically >250 mAh g−1) and low cost.4,5 However, the commercial application of these materials has been hindered by a series of obstacles, including large first-cycle irreversible capacity loss, poor long-term performance, and limited rate capability. Three main reasons are responsible for these issues:6 (i) net loss of Li2O from the Li2MnO3 component, (ii) unstable surface properties and dissolution of transition metals at high potentials, and (iii) low ionic and electronic conductivities of the Li2MnO3 component. Some promising approaches, including surface coating,7 nanoengineering,8 and increasing the Li+ diffusion channels,9 have been explored to minimize these issues. Surface coating is effective for improving the cycling performance of the lithiumrich layered oxides, but it adversely affects the capacity and rate capability because most coating materials are insulators and electrochemically inert. Reducing the particle size to nanoscale can improve the rate performance of a material by shortening the Li+ diffusion length. However, this approach sacrifices the structural stability of the material and accelerates the side reactions of electrolytes.10 As a result, the overall performance © 2016 American Chemical Society
Received: July 24, 2016 Accepted: September 23, 2016 Published: September 23, 2016 25654
DOI: 10.1021/acsami.6b09118 ACS Appl. Mater. Interfaces 2016, 8, 25654−25659
Letter
ACS Applied Materials & Interfaces
Figure 1. (a and b) Low-magnification SEM images of the LLO product. (c) SEM image of a single flower-like hierarchical architecture. (d) SEM image of a single pyramid. The inset in part d shows a broken pyramid. (e−i) Elemental mappings and EDX analysis of a single flower-like hierarchical architecture shown in part c. (j) XRD pattern of the LLO product. The inset highlights the superlattice peaks in the 2θ range of 20−23°.
discharge capacity, rate capability, and cyclability as a cathode material for LIBs. The morphology of the LLO synthesized via the solvothermal method using pure ethanol as the solvent and subsequently annealed at 900 °C was investigated by scanning electron microscopy (SEM). SEM images in Figure 1a,b clearly show a uniform flower-like hierarchical architecture with an average size of 20 μm. A high-magnification SEM image in Figure 1c reveals that the unique architecture is constructed from tens of pyramids with a length of around 10 μm. These pyramids are attached to each pyramid, leading to formation of the flower-like structure. This kind of morphology for a lithiumrich layered oxide has never been reported in the literature. Figure 1d shows a typical SEM image of a single pyramid that possesses a hollow structure enclosed by small LLO nanoplates. The hollow interior of the pyramid is further confirmed by SEM images of a broken pyramid (the inset in Figure 1d and Figure S1a,c), which presents a large inner cavity and a well-
of complex HPH-structured lithium-rich layered oxides remains a great challenge. Herein, we report a novel HPH architecture for lithium-rich layered oxides, which has a delicate flower-like morphology consisting of small interconnected nanoplates. This unique hierarchical architecture based on a nanoplate as the primary unit and the hollow structure offers a porous framework, low energy barrier for Li+ transport, and high surface area accessible to the electrolyte, all of which facilitate the charge/discharge reactions in the electrode. Moreover, the presence of a large internal cavity and a highly porous shell can promote diffusion of the electrolyte into the inner space of the material as well as provide sufficient open channels for fast Li+ migration. Above all, this unique structure may bring a step closer to the kinetic requirements for long-term life and fast charging/discharging of an ideal electrode material. The resulting HPH-structured 0.5Li2MnO3·0.5LiMn0.4Co0.3Ni0.3O2 (LLO) shows excellent 25655
DOI: 10.1021/acsami.6b09118 ACS Appl. Mater. Interfaces 2016, 8, 25654−25659
Letter
ACS Applied Materials & Interfaces
Figure 2. (a and d) TEM images of a single LLO pyramid. The insets of parts a and d show the frontal and lateral planes of an individual nanoplate. (b) HRTEM image and (c) SAED pattern of the frontal plane of an individual nanoplate shown in part a. (e) HRTEM image and (f) SAED pattern of the lateral plane of an individual nanoplate shown in part d.
enclosed by well-defined facets. The hollow interior and porous structure consisting of interconnected nanoplates are clearly revealed. The high-resolution TEM (HRTEM) image of the frontal plane of a typical nanoplate (Figure 2b) gives two sets of lattice fringes of 0.417 and 0.424 nm corresponding to the d pacings of the (110) and (020) planes of Li2MnO3, respectively. This result indicates the (002) plane of the Li2MnO3 phase in the frontal plane. The selected-area electron diffraction (SAED) pattern of the corresponding area (Figure 2c) shows 6-fold symmetry, which reflects the hexagonal structure of the LiMn0.4Ni0.3Co0.3O2 phase and can be assigned to its (001) plane.8,15 These results suggest that the frontal plane of the nanoplate is comprised of the (002) plane of the Li2MnO3 phase and the (001) plane of the LiMn0.4Co0.3Ni0.3O2 phase. Figure 2e displays lattice fringes of a lateral plane with interplanar distances of 0.243 and 0.476 nm, corresponding to the (101) and (003) planes of the LiMn0.4Co0.3Ni0.3O2 phase, respectively.9 This observation indicates that the lateral plane investigated is the (010) plane of the LiMn0.4Co0.3Ni0.3O2 phase, which is also supported by the corresponding SAED pattern in Figure 2f. The other five lateral planes are (010̅ ), (1̅00), (11̅0), (110), and (100), which can be deduced on the basis of the hexagonal structure of the LiMn0.4Co0.3Ni0.3O2 phase. These {010} lateral planes with an open structure between the transition-metal layers are normal to the facile pathway for Li+ migration and electrochemically active.22 Furthermore, it should be noted that the structural feature of the Li2MnO3 phase is not observed in the lateral plane because the reflections of the Li2MnO3 and LiMn0.4Co0.3Ni0.3O2 phases viewed along the [010], [110], and [100] orientations are overlapping.23 The HRTEM results and SAED pattern clearly demonstrate the coexistence of LiMn0.4Co0.3Ni0.3O2 and Li2MnO3 in the LLO. All of the characterization results demonstrated the successful fabrication of the hollow, porous, and flower-like hierarchical-structured LLO with the desired chemical composition and well-ordered structure.
defined shell. The small primary nanoplate has a hexagonal-like shape with an edge length of 100−250 nm and a thickness of ∼150 nm (Figure S1b,d). The corresponding energy-dispersive X-ray (EDX) elemental mappings of a single microflower and pyramid (Figures 1e−h and S2) suggest the uniform distribution of oxygen, manganses, cobalt, and nickel within them. The elemental mapping of the large area (Figure S3) further verifies that these elements are homogeneously distributed within the material. The atomic ratios of manganese, cobalt, and nickel estimated from the EDX spectra (Figure 1i) and inductively coupled plasma atomic emission spectroscopy (ICP-OES; Table S1) are almost identical with the feeding ratio of 0.56:0.12:0.12 (Figures 1I and S2b and S3b). The X-ray diffraction (XRD) pattern of LLO is shown in Figure 1j. All the strong peaks belong to a hexagonal α-NaFeO2 structure with R3m ̅ symmetry, which is normally taken as the signature of the LiMO2 phase. Three weak peaks between 20 and 23° (2θ) are consistent with the superlattice ordering of lithium and manganese in the transition-metal layers of the Li2MnO3 phase and can be assigned to its (020), (1̅11), and (110) planes.19 The clear splitting of the adjacent peaks of (006)/(012) and (108)/(110) and a high (>1.5) intensity ratio of I(003)/I(104) imply a highly ordered layered LLO (Figure S4).20 The oxidation states of manganese, cobalt, and nickel in the as-synthesized LLO were studied using X-ray photoelectron spectroscopy (XPS), and the corresponding spectra are illustrated in Figure S5. The observed binding energies of these elements are consistent with the values reported for similar materials.21 The main peaks at binding energies of 642, 780, and 855 eV are attributed to Mn4+, Co3+, and Ni2+, respectively. The microstructure of the LLO product was further characterized by transmission electron microscopy (TEM). Parts a and d of Figure 2 show that the pyramid is formed by the oriented aggregation of small hexagonal nanoplates 25656
DOI: 10.1021/acsami.6b09118 ACS Appl. Mater. Interfaces 2016, 8, 25654−25659
Letter
ACS Applied Materials & Interfaces
The formation process mainly involves two steps: (1) formation of the solid flower-like precursor by a solvothermal reaction; (2) conversion of the solid precursor into the hollow porous flower-like LLO by a high-temperature sintering process. During synthesis of the precursor, ethanol is believed to play an important role as discussed above. Previous studies have demonstrated that polar alcohols can chelate with metal ions, slowing down the reduction kinetics.25,26 In addition, ethanol molecules can selectively adsorb on some specific facets of the nuclei via a negatively charged CH3CH2O− group and slow down their growth. The preferential adsorption of the CH3CH2O− group on specific facets results in the selective deposition of metal atoms on uncapped surfaces. Furthermore, the solvothermal process also plays a crucial role in the formation of a solid flower-like precursor. During the solvothermal process, the long-lasting (12 h), high-temperature (180 °C) treatment can promote the growth of uncapped surfaces and accelerate the formation process of the solid flower-like precursor. In the final step, thermal calcination at 900 °C is applied, during which the precursor is completely converted into LLO. Interestingly, the final LLO product still retains the flower-like shape but exhibits a hollow porous texture and rough surface constructed by many small nanoplates. The transformation from a solid to a hollow porous structure during the high-temperature calcination process is attributed to thermal decomposition of the precursor according to the reaction Li−Mn−Co−Ni−C 2 O 4 → Li1.2Mn0.56Co0.12Ni0.12O2 + CO2. The release of CO2 may be responsible for the formation of the porous structure. Meanwhile, a Kirkendall-effect-like mechanim involving the fast outward diffusion of lithium, manganese, cobalt, and nickel atoms and the slow inward diffusion of oxygen atoms, together with fusion of the precursor at high temperatures, might be the reason for the formation of the hollow cavity.27 On the basis of the above analysis, we conclude that ethanol, solvothermal reaction, and thermal calcination are keys to forming the HPHstructured flower-like LLO. It should be noted that the formation mechanism of the hierarchical-structured LLO could be much more complicated. To demonstrate its potential applications in LIBs, the electrochemical performance of the HPH-structured LLO was evaluated as the cathode active material in coin cells. The rate capability of the LLO at current rates ranging from 0.2 to 10 C between 2.0 and 4.8 V is displayed in Figure 4a,b. Impressively, the HPH-structured LLO exhibits a remarkably high rate capability, which is highly desired for high-power LIB applications such as hybrid and full electric vehicles. The discharge capacities are 296.5, 270.6, 243.6, 207.8, and 187.4 mAh g−1 at rates of 0.2, 0.5, 1, 3, and 5 C, respectively. Even at a high rate of 10 C, an excellent discharge capacity as high as 162.6 mAh g−1 is achieved. The error bar of the discharge capacity at different rates is around 5 mAh g−1 in five parallel tests. These capacities are remarkably higher compared with those previously reported for lithium-rich layered oxides (Table S2). Such high discharge capacities might be associated with the unique structure of the hollow LLO with porous shells, which can afford a large electrochemical active surface and allow a large Li+ flux across them. More importantly, after high rate measurements, a high discharge capacity of 283.6 mAh g−1 (compared with the original value of 296.5 mAh g−1) can still be achieved once the rate is returned to 0.2 C, indicating a high rate capability and structure stability of the material.
To further understand the formation process of the unique HPH structure, the morphology and crystal structure of the precursor were also studied by SEM, TEM, and XRD (Figures S6 and S7). The panoramic SEM image of the precursor (Figure S6a) shows flower-like structures with a size of about 20 μm. Magnified SEM images (Figure S6b,c) clearly disclose that they are composed of about 10 pyramids (∼10 μm in length) with smooth surfaces. In contrast to the hollow porous structure of the LLO, the solid and dense nature of the flowerlike precursor is demonstrated by the TEM image of a typical pyramid (Figure S6d). The XRD pattern of the precursor is shown in Figure S5. The main peaks can be readily indexed to the Li2C2O4, MnC2O4·2H2O, NiC2O4·2H2O, and CoC2O4· 2H2O phases, which are the most probable structures that can be formed during the solvothermal process. It has been known that solvents play a critical role in determining the morphology of the nano- and microstructures.24 In our case, when water was used as the solvent, the precursor showed a rhombic shape with an edge length of ∼2 μm (Figure 3a). After calcination, the morphology of the
Figure 3. (a and c) SEM images of the precursor and LLO prepared by the solvothermal method using water as the solvent, respectively. (b and d) SEM images of the precursor and LLO prepared by the solvothermal method using 1:1 water/ethanol as the solvent, respectively.
precursor changed completely. The final LLO product was mainly composed of irregular particles with a diameter of ∼1 μm (Figure 3c). When 1:1 water/ethanol was used as the solvent, the precursor had a cuboid shape with six rectangular facets and sharp edges (Figure 3b). The length of the cuboid was in the range of 7−10 μm. After calcination, the cuboid changed to a rodlike aggregate that was composed of many irregular particles (Figures 3d and S8). These results indicate that the morphologies of the precursor and final product are strongly dependent on the solvents used in the synthesis. Only pure ethanol was found to be effective in producing a flowerlike hierarchical structure in the current solvothermal synthesis. On the basis of the above discussion, the formation of HPHstructured flower-like LLO could be explained by a solventinduced oriented attachment growth mechanism together with the Kirkendall effect, as schematically depicted in Figure S9. 25657
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performance of the LLO is thus significantly improved. The tap density of the as-prepared hollow porous LLO is ∼1.0 g cm−3, which is lower than that of spherical LLO (1.6−1.8 g cm−3).21,29 Further improvement on the volumetric capacity is required. In summary, novel HPH-structured lithium-rich layered oxides have been successfully synthesized and evaluated as cathode materials for LIBs. This novel architecture is constructed with interconnected nanoplates and possesses a hollow porous texture. Owing to the large interior space, open surface structure, robust hierarchical architecture, and small primary nanoparticles, the as-prepared LLO shows exceptional electrochemical performance with excellent discharge capacity, rate capability, and cyclability. This work demonstrated the importance of the structure of the active materials on their electrochemical performance in LIBs.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b09118. Details of the synthetic procedure, SEM images of a broken flower-like hierarchical architecture (Figure S1), SEM images and EDX analysis of a single pyramid and LLO product (Figures S2 and S3), chemical composition of the LLO product measured by ICP-OES (Table S1), magnified XRD patterns and XPS spectra of the LLO product (Figures S4 and S5), SEM and TEM images and XRD pattern of the precursor of Li−Mn−Ni−Co−C2O4 (Figures S6 and S7), SEM image of the LLO prepared by the solvothermal method using 1:1 water/ethanol as the solvent (Figure S8), schematic illustration of the formation process of HPH-structured LLO (Figure S9), comparison of the properties between the LLO of this study and reported lithium-rich layered oxides (Table S2), charge/discharge voltage profiles at rates of 0.2 and 0.5 C (Figure S10), and SEM images of LLO after potential cycling (Figure S11) (PDF)
Figure 4. Electrochemical performance of the LLO product as a cathode material in LIBs: (a) charge/discharge voltage profiles at various rates from 0.2 to 10 C in the voltage range of 2.0−4.8 V; (b) rate performance; (c) cycling performance and corresponding Coulombic efficiency at 0.2 C for 2 cycles and then at 0.5 C for 100 cycles; (d) cycling performance and corresponding Coulombic efficiency at a high rate of 10 C. 1 C = 200 mA g−1.
The extraordinary cycling performance of the HPHstructured LLO was further examined by charging/discharging in the voltage range of 2.0−4.8 V. Figure 4c shows the cycling performance of the HPH-structured LLO at 0.2 C for 2 cycles and then at 0.5 C for 100 cycles. The average discharge capacity for the first two cycles (activation) at 0.2 C is 292.7 mAh g−1 (Figure S10a). After activation, the cathode was cycled at 0.5 C, with discharge capacities of 272.6, 247.6, and 237.6 mAh g−1 for the 3rd, 50th, and 100th cycles, respectively (Figure S10b). The capacity retention is over 87% after 100 cycles with a capacity fading rate of 0.13% per cycle. Even at a much higher rate of 10 C, the HPH-structured LLO can still deliver a discharge capacity of 153.8 mAh g−1 with a negligible decay over 200 cycles (Figure 4d). The increase of the capacity in the first 30 cycles (topped at 158.3 mAh g−1) is due to slow activation of the LLO in the electrode at 10 C. Moreover, the SEM image reveals that the initial HPH structure can be well maintained after cycling at 0.5 C for 100 cycles (Figure S11), indicating its outstanding structural robustness. The excellent battery performance of the as-prepared HPHstructured LLO might be attributed to its unique structural characteristics. Specifically, the increased area of the hollow structure provides sufficient active sites for electrochemical reaction and high Li+ flux across the interface. The presence of thin porous shells and small primary nanoparticles makes Li+ migration much easier by shortening the diffusion length effectively.28 Meanwhile, the robust micron-sized hierarchical architecture can minimize the collapse of the 3D structure during repeated charge/discharge cycling. With enhanced transport kinetics and structural stability, the electrochemical
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work is supported by a startup fund from the Hong Kong University of Science and Technology. REFERENCES
(1) Liu, W.; Oh, P.; Liu, X.; Lee, M. J.; Cho, W.; Chae, S.; Kim, Y.; Cho, J. Nickel-Rich Layered Lithium Transition-Metal Oxide for HighEnergy Lithium-Ion Batteries. Angew. Chem., Int. Ed. 2015, 54, 4440− 4457. (2) Li, X. F.; Liu, J.; Banis, M. N.; Lushington, A.; Li, R. Y.; Cai, M.; Sun, X. L. Atomic Layer Deposition of Solid-State Electrolyte Coated Cathode Materials with Superior High-Voltage Cycling Behavior for Lithium Ion Battery Application. Energy Environ. Sci. 2014, 7, 768− 778. (3) Li, X. F.; Liu, J.; Meng, X. B.; Tang, Y. J.; Banis, M. N.; Yang, J. L.; Hu, Y. H.; Li, R. Y.; Cai, M.; Sun, X. L. Significant Impact on Cathode Performance of Lithium-Ion Batteries by Precisely Controlled 25658
DOI: 10.1021/acsami.6b09118 ACS Appl. Mater. Interfaces 2016, 8, 25654−25659
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ACS Applied Materials & Interfaces Metal Oxide Nanocoatings via Atomic Layer Deposition. J. Power Sources 2014, 247, 57−69. (4) Devaraj, A.; Gu, M.; Colby, R.; Yan, P.; Wang, C. M.; Zheng, J. M.; Xiao, J.; Genc, A.; Zhang, J. G.; Belharouak, I.; Wang, D.; Amine, K.; Thevuthasan, S. Visualizing Nanoscale 3D Compositional Fluctuation of Lithium in Advanced Llithium-Ion Battery Cathodes. Nat. Commun. 2015, 6, 8014. (5) Qiu, B.; Zhang, M. H.; Wu, L. J.; Wang, J.; Xia, Y. G.; Qian, D. N.; Liu, H. D.; Hy, S.; Chen, Y.; An, K.; Zhu, Y. M.; Liu, Z. P.; Meng, Y. S. Gas-Solid Interfacial Modification of Oxygen Activity in Layered Oxide Cathodes for Lithium-Ion Batteries. Nat. Commun. 2016, 7, 12108. (6) Lu, P.; Yan, P. F.; Romero, E.; Spoerke, E. D.; Zhang, J. G.; Wang, C. M. Observation of Electron-Beam-Induced Phase Evolution Mimicking the Effect of the Charge-Discharge Cycle in Li-Rich Layered Cathode Materials Used for Li Ion Batteries. Chem. Mater. 2015, 27, 1375−1380. (7) Sun, Y. K.; Lee, M. J.; Yoon, C. S.; Hassoun, J.; Amine, K.; Scrosati, B. Core-Shell Layered Double Hydroxide Microspheres with Tunable Interior Architecture for Supercapacitors. Adv. Mater. 2012, 24, 1192−1197. (8) Chen, L.; Su, Y. F.; Chen, S.; Li, N.; Bao, L. Y.; Li, W. K.; Wang, Z.; Wang, M.; Wu, F. Hierarchical Li1.2Ni0.2Mn0.6O2 Nanoplates with Exposed {010} Planes as High-Performance Cathode Material for Lithium-Ion Batteries. Adv. Mater. 2014, 26, 6756−6760. (9) Wei, G. Z.; Lu, X.; Ke, F. S.; Huang, L.; Li, J. T.; Wang, Z. X.; Zhou, Z. Y.; Sun, S. G. Crystal Habit-Tuned Nanoplate Material of Li[Li1/3−2x/3NixMn2/3−x/3]O2 for High-Rate Performance Lithium-Ion Batteries. Adv. Mater. 2010, 22, 4364−4367. (10) Yu, L.; Zhang, L.; Wu, H. B.; Zhang, G. Q.; Lou, X. W. Controlled Synthesis of Hierarchical CoxMn3−xO4 Array Micro/ nanostructures with Tunable Morphology and Composition as Integrated Electrodes for Lithium-Ion Batteries. Energy Environ. Sci. 2013, 6, 2664−2671. (11) Choi, S. H.; Kang, Y. C. Ultrafast Synthesis of Yolk-Shell and Cubic NiO Nanopowders and Application in Lithium Ion Batteries. ACS Appl. Mater. Interfaces 2014, 6, 2312−2316. (12) Ye, J. F.; Liu, W.; Cai, J. G.; Chen, S.; Zhao, X. W.; Zhou, H. H.; Qi, L. M. Nanoporous Anatase TiO2 Mesocrystals: Additive-Free Synthesis, Remarkable Crystalline-Phase Stability, and Improved Lithium Insertion Behavior. J. Am. Chem. Soc. 2011, 133, 933−940. (13) Zhang, L. J.; Li, N. B.; Wu, R.; Xu, H. L.; Wang, L.; Yang, X. Q.; Wu, F. Sphere-Shaped Hierarchical Cathode with Enhanced Growth of Nanocrystal Planes for High-Rate and Cycling-Stable Li-Ion Batteries. Nano Lett. 2015, 15, 656−661. (14) Zhang, Y. D.; Li, Y.; Niu, X. Q.; Wang, D. H.; Zhou, D.; Wang, X. L.; Gu, C. D.; Tu, J. P. A Peanut-Like Hierarchical Micro/nano Li1.2Mn0.54Ni0.18Co0.08O2 Cathode Material for Lithium-Ion Batteries with Enhanced Electrochemical Performance. J. Mater. Chem. A 2015, 3, 14291−14297. (15) Wang, D. P.; Belharouak, I.; Zhou, G. W.; Amine, K. Nanoarchitecture Multi-Structural Cathode Materials for High Capacity Lithium Batteries. Adv. Funct. Mater. 2013, 23, 1070−1075. (16) Liu, J. L.; Hou, M. Y.; Yi, J.; Guo, S. S.; Wang, C. X.; Xia, Y. Y. Improving the Electrochemical Performance of Layered Lithium-Rich Transition-Metal Oxides by Controlling the Structural Defects. Energy Environ. Sci. 2014, 7, 705−714. (17) Yu, L.; Zhang, L.; Wu, H. B.; Lou, X. W. Formation of NixCo3−xS4 Hollow Nanoprisms with Enhanced Pseudocapacitive Properties. Angew. Chem., Int. Ed. 2014, 53, 3711−3714. (18) Yang, W. L.; Zhang, L.; Hu, Y.; Zhong, Y. J.; Wu, H. B.; Lou, X. W. Microwave-Assisted Synthesis of Porous Ag2S-Ag Hybrid Nanotubes with High Visible-Light Photocatalytic Activity. Angew. Chem., Int. Ed. 2012, 51, 11501−11504. (19) Long, B. R.; Croy, J. R.; Dogan, F.; Suchomel, M. R.; Key, B.; Wen, J. G.; Miller, D. J.; Thackeray, M. M.; Balasubramanian, M. Effect of Cooling Rates on Phase Separation in 0.5Li2MnO3·0.5LiCoO2 Electrode Materials for Li-Ion Batteries. Chem. Mater. 2014, 26, 3565−3572.
(20) Thackeray, M. M.; Kang, S. H.; Johnson, C. S.; Vaughey, J. T.; Hackney, S. A. Comments on the Structural Complexity of LithiumRich Li1+xM1−xO2 Electrodes (M = Mn, Ni, Co) for Lithium Batteries. Electrochem. Commun. 2006, 8, 1531−1538. (21) Li, B.; Yu, Y. Y.; Zhao, J. B. Facile Synthesis of Spherical xLi2MnO3·(1-x)Li(Mn0.33Co0.33Ni0.33)O2 as Cathode Materials for Lithium-Ion Batteries with Improved Electrochemical Performance. J. Power Sources 2015, 275, 64−72. (22) Fu, F.; Wang, Q.; Deng, Y. P.; Shen, C. H.; Peng, X. X.; Huang, L.; Sun, S. G. Effect of Synthetic Routes on the Rate Performance of Li-rich Layered Li1.2Mn0.56Ni0.12Co0.12O2. J. Mater. Chem. A 2015, 3, 5197−5203. (23) Yu, H. J.; So, Y. G.; Kuwabara, A.; Tochigi, E.; Shibata, N.; Kudo, T.; Zhou, H. S.; Ikuhara, Y. C. Crystalline Grain Interior Configuration Affects Lithium Migration Kinetics in Li-Rich Layered Oxide. Nano Lett. 2016, 16, 2907−2915. (24) Yu, B. B.; Zhang, X.; Jiang, Y.; Liu, J.; Gu, L.; Hu, J. S.; Wan, L. J. Solvent-Induced Oriented Attachment Growth of Air-Stable PhasePure Pyrite FeS2 Nanocrystals. J. Am. Chem. Soc. 2015, 137, 2211− 2214. (25) Sun, C. W.; Rajasekhara, S.; Goodenough, J. B.; Zhou, F. Monodisperse Porous LiFePO4 Microspheres for a High Power Li-Ion Battery Cathode. J. Am. Chem. Soc. 2011, 133, 2132−2135. (26) Yang, H. G.; Liu, G.; Qiao, S. Z.; Sun, C. H.; Jin, Y. G.; Smith, S. C.; Zou, J.; Cheng, H. M.; Lu, G. Q. Solvothermal Synthesis and Photoreactivity of Anatase TiO2 Nanosheets with Dominant {001} Facets. J. Am. Chem. Soc. 2009, 131, 4078−4083. (27) Zhou, L.; Zhao, D. Y.; Lou, X. W. LiNi0.5Mn1.5O4 Hollow Structures as High-Performance Cathodes for Lithium-Ion Batteries. Angew. Chem., Int. Ed. 2012, 51, 239−241. (28) Zhong, Y. R.; Yang, M.; Zhou, X. L.; Zhou, Z. Structural Design for Anodes of Lithium-Ion Batteries: Emerging Horizons from Materials to Electrodes. Mater. Horiz. 2015, 2, 553−566. (29) Martha, S. K.; Nanda, J.; Veith, G. M.; Dudney, N. J. Surface Studies of High Voltage Lithium Rich Composition: Li1.2Mn0.525Ni0.175Co0.1O2. J. Power Sources 2012, 216, 179−186.
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